The present invention relates to the field of transmissions, and more specifically, to sun gear shell assemblies used in automatic transmissions of vehicles.
In vehicle automatic transmissions of types TH700, 4L60, 4L60E, conventional original equipment manufacturing (OEM) designs of sun shells 10 use cold-rolled, low carbon steel of the type SAE 1010-1020 for the shell body 11, with the shell body 11 being stamped as one piece (see FIG. 1). However, the sun gear shell 10 used in these transmissions has a history of a high failure rate.
The majority of the failures of the OEM design includes failure at the neck collar 12 of the spline 13 (see FIG. 2) because high stress is concentrated at this point. Specifically, in conventional designs, the neck 12, which is supported on a circular, raised area 14 on an end surface 15 of the shell body 11, is formed unitarily with the shell body 11, with a 90 degree angle formed between the neck 12 and the raised area 14 of the shell body 11. High stress concentration and a weak neck base 12 result in a fatigue problem.
Further, the neck collar design, with the neck 12 being relatively thin and having an outside diameter of D1=60.00 mm, and with the use of thin, weak, materials such as low carbon steel at a thickness of d1=3.00 mm for the sun gear shell body 11, limit the strength of the neck collar 12 and the body 11 of the shell 10.
Still further, the engaging lugs 31 of the shell 10, mushroom due to the use of the thin material for the shell 10, and due to strong operational impact, causing failure of the sun gear shell 10.
Accordingly, an object of the present invention is to provide a sun gear shell and sun gear shell assembly which is sturdier than previous conventional designs, and which virtually eliminates the high incidence of failures, particularly at the neck.
Specifically, the sun gear shell includes a cylindrical shell body formed by cold-rolling a low carbon steel, and a neck section having a protruding neck collar, formed by heat drawing and machining a middle carbon steel. The middle carbon steel of the neck section is stronger than the low carbon steel of the shell body. The wall thickness of the shell body is increased for added strength. The neck base has a 30 degree chamfer to prevent failures at the neck section, and the neck section is then welded to the shell body so that the sun gear shell becomes a single piece. A plurality of holes are disposed in the neck section encircling the neck collar.
In another aspect of the invention, the sun gear shell assembly includes the sun gear shell as described above, and an injection molded plastic washer having a plurality of tabs on one side surface. The plastic washer has the tabs inserted into holes formed in the neck section of the sun gear shell to form the complete sun gear shell assembly.
The method of manufacturing the sun gear shell, includes deep cold drawing the low carbon steel to form a wall of a cylindrical shell body; forming a neck section having a protruding neck with an enforced corner chamfer, using the middle carbon steel; punching out a plurality of holes encircling the neck; and welding the neck section onto the shell wall to make the sun gear shell become a one-piece construction.
In another aspect of the present invention, the method of manufacturing the sun gear shell assembly includes manufacturing the sun gear shell, and also injection molding a plastic washer having a plurality of tabs on one side surface. To complete the manufacture of the complete sun gear shell assembly, the tabs of the plastic washer are inserted into the holes formed in the neck section.
These modifications to the conventional sun gear shell assembly eliminate the high failure rate at the neck section and provide additional strength to the sun gear shell assembly.
There has thus been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract included below, are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.